This invention relates to gas-filled disconnecting switch which includes a resistor for suppressing an abnormal voltage and is capable of interrupting a loop current.
In electric power substations, the disconnecting switch is normally located adjacent to an associated circuit breaker and is typically used (1) to open and close a line disconnected by the circuit breaker and (2) to switch transmission systems. For the former function (1), the disconnecting switch is operative to open and close an electric line under non-loading conditions and it is known that the restrike of an electric arc is repeated across a pair of opposite contact members of the disconnecting switch to generate sharp so-called disconnecting switch-surges. This is because the disconnecting switch has a switching speed which is relatively low as compared with the switching speed of the circuit breaker. It is also well known to provide the disconnecting switch with a resistor for suppressing such opening and closing surges.
On the other hand, the latter function (2) serves to switch power from one to another of bus bars in the associated substation by use of the disconnecting switch. For example, where a pair of bus bars are connected to a common line through respective disconnecting switches, the operation of switching from one to the other of the bus bars results in the interruption of the so-called loop current which approximates a rated current flowing through a circuit including the pair of disconnecting switches, by utilizing the good interrupting ability exhibited by a sulfur hexafluoride (SF.sub.6). This is also well known.
Furthermore both the ability to open and close a line under non-loading conditions and the ability to open and close the loop current as described above are required, in many cases, for a common disconnecting switch to be disposed within a substation.
A conventional disconnecting switch including a resistor for suppressing surges upon opening and closure is disclosed, for example, in Japanese laid-open patent application No. 95,276/1978. According to the cited application, the prior disconnecting switch includes an envelope filled with a sulfur hexafluoride (SF.sub.6) gas, an electrically conducting support member extended and sealed through one end of the envelope, and a main stationary contact member and an arcing stationary contact member are coaxially disposed on the support member. Also a hollow cylindrical resistor is disposed on the support member to coaxially surround the main stationary contact member and includes a free end portion terminating at a metallic shield in the form of a semitoroid located above the main stationary contact member and surrounding the arcing stationary contact member. A movable contact member in the form of a hollow cylinder is disposed to oppose to the main and arcing stationary contact members and separably engage them by having one end portion thereof separably sandwiched therebetween.
Upon disengaging the movable contact member from the main and arcing stationary contact members, scores of restruck electric arcs are intermittently caused across the shield and the extremity of the movable contact member, resulting in the occurrence of high sharp surges which are reduced by the hollow cylindrical resistor. This is true in the case of the engagement of the movable contact member with the main and arcing stationary contact members. Also the restruck arc has resulted in damages to the shield.
Furthermore an electric field established adjacent to the cylindrical resistor has abruptly changed immediately after the occurrence of a restruck electric arc as compared with that established before the occurrence of the restruck arc. This has resulted in a rapid increase in electric field intensity from the shield or support member directed to the envelope. Thus, this rapid increase in electric field intensity has progressed with high probability to a short circuit-to-ground fault.
Accordingly, it is an object of the present invention to provide a new and improved disconnecting switch, capable of preventing the shield from being damaged due to a restruck electric arc caused upon the opening and closure thereof, and substantially free from a change in electric field established adjacent a stationary contact side immediately after the occurrence of the restruck electric arc.